Pull-off magnet



PULL-OFF MAGNET Filed 'Jan. 7, 1944 I nventor: 30 I I Richard 6. Jewel I,

' His Attorney Patented May 28, 1946 PULL-OFF MAGNET Richard G. Jewell, S wampscott, Mass, assignor to General Electric Company, a corporation of New York Application January 7, 1944, Serial No. 517,419

' BClaims. (01. 171-95) My invention relates to auxiliary magnetic torque producing arrangements particularly dethe following description to the accompanying drawing in which Fig. 1 shows a plan view of the auxiliary torque producing unit; Figs. 2, 3, and 3a are side views of strips of permanent magnet material used before being bent into a circular form; Fig. 4 shows the application of my invention to provide the zero return and pull-off torque of a diflerential electrical measuring instrument; Figs. 5 and 6 are plan and partial side views of a zero center scale instrument to which my invention is applied; and Fig. 7 represents. my invention where the c-shaped magnet of my invention is on the shaft of an instrument of the stationary permanent type.

In Fig. 1, it] represents a sector-shaped permanent magnet which may be formed by taking a strip of suitable permanent magnet material such as shown in Fig. 2, and bending it into the form of a. nearly closed. relatively thin circular band, as shown in Fig. l. The strip will preferably have a uniform thickness but will vary in height. The strip shown in Fig. 2 has its greatest height at the center It and tapers uniformly toward its ends. The strip is preferably bent so that its uniform dimension is radial and graduated dimensions axial. This magnet is permanently magnetized in-a radial direction as shown in Fig. l with one pole N outside and the other pole S inside. The material is polarized to have a uniform flux density or strength per unit area but since the area is not uniform, the magnet will be strongest at the center .H and will have a uniform decrease in magnetic strength in both directions from center until the ends at the opening I! in the circle are approached. Pivoted at the center I! of the circle outlined by the magnet I0 is another permanent magnet I 4 which is preferably but not necessarily of bar shape. The rotary magnet is polarized to have its magnetic axis diametrically of the circle and-axis of rotation, or in the case of a bar magnet, pivoted at its center as shown in Fig. 1, along its major axis. The length of the magnet H is somewhat less than the inner diameter of the circle outlined by the circular magnet.

It is now evident that the radial south pole throughout the length of the inside of the circular magnet will attract the north pole of the pivoted magnet and repel its south pole. Since the south pole of the circular magnet is strongest or has greatest flux at its center I l and is weakest at the opening [2, the pivoted magnet will rotate until its north pole end is opposite center ll of the circular magnet. For instance. in the position shown in Fig. 1, there is a clockwise torque on the rotor magnet as indicated by the arrows. Since this torque is proportional to the rate of change, of radial cross-sectional area of the circular magnet, it is uniform over a large Dart of the 360 degrees except as the rotary magnet approaches near to the neutral position. If magnet H has its position reversed in Fig. 1,, this uniform torque will be counterclockwise instead of clockwise. Thus it is possible to provide a substantially uniform torque in this way over arcs of about degrees in opposite directions.

Also, the torque can he graduated or tailored from the constant value described by departing from the uniform rate of change in cross-section of the circular magnet, and in Fig. 3, I have shown the development of a magnet where the cross-section from center varies nonuniformly but symmetrically, and in Fig. 3a. a shape is shown which is nonsymmetrical both with respect to the shape on opposite sides of the point of maximum cross-section and with respect to the oil-center point of maximum cross-section. If this magnet is used in Fig. 1. the rotary magnet will have a zero torque position at about point it because of the torque effect at the open ends of the circle. Such auxiliary torque device is useful in indicating instruments for obtaining a pull-oil torque, a zero return torque. to modify the scale distribution, etc. further variations in torque can be obtained by positioning the magnet Ill oil center with respect to the armature H and by oval or noncircularshaped magnets I ll.

It should he mentioned that a permanent mag net material should be used for the curved magnet that hashigh coercive force and low permeability. and preferably, a material that can be readily bent as described. One material which is in United States Letters Patent to Fans No. I

2,247,804, July 1, 1941.

It will of-course be evident that In Fig. 4 I have shown an electrical measuring is positioned opposite the proper pole of armature instrument which may comprise the receiver of magnet 14 when at the zero center position as a. telemetering system and to which my invention shown. Fig. 6 shows a partial plan view of the is applied to provide zero return and pul1-0ff same instrument to show how the zero return torque. Also, the permanent rotor magnet pretorque may be adjusted by moving the circular viously described is also the armature of the magnet ill axially toward and away from the receiver. The instrument has two stationary armature magnet M by an adjusting device '39. radial axis coils l6 and H energized dii'feren- It is noted that the magnet lfl.-hae a convex tialLv from a direct-current source id in accurvature from its largest center part to its open cordance with the position of a transmitter mem-- ends in order to make the zero return torque her which moves to contact I9 along a resistance increase with the deflection from zero and the 20. Assuming the coils l and I! produce N pole instnunent stable. fluxes adajacent the armature ll, the south pole In any case where the armai' ire oi the iuof such polarized armature will be attracted and ctrument used is not of the pol t me will swing toward that soil ll most strongly enone wishes to apply invention ergized at the moment, end W1 take various magnet separated cm the all cg the merit of the ti" 2! moving over fit scale ii cordinglyt *lhi elements of or H, the pointer indication Will the zero end thereof and will line 23. Thus in case power coils I6 and i1 without out that the our direction to i from any p-o "u the scale one. may

- measuring to justeci relative to the auxilict pointer will he on zero. The z-xllia-ry torque is independent of and supplerrlentul to the instrument torque '94: our o diaxnctl'icel magnet iiielil symmetrically with respect to the axis of rotation but along one axis only, the poles I have 3 represented at u rmg made of opposite magnetic polarity of the last-menof conducting material such as brass or copper tioned ma t hen 1 w 1 t d fitted inside the circular magnet 10. This profine g anemls y a rides a limited amount of dumping for the inand repelled by the magnetm field of one polarity strumcnt and also some protection to the magnet of the {curved the fame of magnet: 10 against demagnetization. It is not essential attractwn and.repu1smn between said i but its use my be desirable in some instances varying with dlfierent relatively rotary IJOSl'LiOXlS As an alternative the circular magnet may be of Said magnets q 150mm is devel' plated with a heavy coating of copper. oped between them in certain positions.

In Fig. 5 I have Shown a direct current An auxiliary torque device as claimed in strument of the zero center type for measuring 01mm which the curved magnet} current and the direction of such current. It shaped m ,band 9 constant radial, thlck" may be used for example to measure the charg ness and of varying axial thickness polar zed raing or discharge current of a battery 25 and the (any at substantially uniform? flux density coils 2c and 21 connected in the battery circuit An .auxmary dell as in in series so that the con 26 produces South claim in which the curved magnet is stationpole adjacent the armature l4 and the coil IT My and 1S locaf'ted outslde the 01mm magnet produces a north pole adjacent the -armature can auxiliary'torque device as claimed in H when the battery current is in one direction. claim in which the curvgd magnet is m the In such case the pointer 2| Win deflect to the form of a circular c-shaped bond, is stationary left of the zero center Scale it w the cup and located externally of the other magnet with t reverses, t mt 111 deflect t h right its circular arc concentric with the axi of rotaof zero. My auxiliary torque feature is here used lion of the other ma to provide the zero center return torque and a 5. An auxiliary torque device es claimed in deflection proportional to the measurement in claim 1, in which the curved magnet is in the either direction. For this purpose the large :iorm of a substantially circular- C-shaped band cross-sectional center ll of the circular magnet 7: of uniform radial thickness and with greatest axial thickness at its center and tapering sym-' instrument and polarized to produce a symmetrical diametrical flux in one axis at right angles to its axis of rotation, an auxiliary torque device instrument comprising a stationary o-shaned permanent magnet surrounding the axis or? rotation of said instrument outside of the armature thereof, said ei-shaped magnet being poiarizcd radially so as to produce attraction with respect one pole of said armature and repulsion with respect to the other pole of said armature, the rediai iiux strength of said C shaped magnet graduated about the axis of rotation so or to produce a rotary torque on said ermatui considerahie portion. oi the range of n of said armature.

2. In an eiectrical, measuring instrument hav ing cooperating coil. and permanent magnet memhers which are relatively rotatable with respect to each other about a common axis of rotntion for producing electrical measurement dc fleet-ion operations, the magnet producing a iiux diametrically "with respect to the axis of rota tion of said instrument, an auxiliary torque de vice for said instrument comprising a Lt-shaped permanent magnet mounted in fixed relation to the coil member of said measuring instrument, said (i-shaped permanent magnet being substantially coaxial with and surrounding the axis of rotation of said instrument and being poiarized radially throughout its circular length so a simultaneously to produce repulsion torque with respect to one magnet pole of said instrument permanent magnet member and attraction torque with the other magnetic pole thereof, the flux strength of said C-shaped magnet being graduated about the axis of rotation of the instrument, and said'c-shaped magnet and instrument permanent magnet member being so rota-- tively positioned with respect to each othenas to cause the c-shaped magnet to produce desirable rotary torque on the rotary member of said instrument which-1s independent of and supplemental to the instrument measurement torque thereof over substantially the complete measurement range or operation or said instrument.

8. In an electrical measuring instrument having an axis of rotation established by relatively rotatable electrical measurement members one of which comprises a coil member and the other mean for producing a constant unidirectional field diametrically of the axis of rotation of said instrument and means for producing a desirable auxiliary torque in said instrument comprising a C-shaped permanent magnet surrounding the axis of rotation of said instrument within the influence of the constant unidirectional field thereof, said -Q=Ei3mfed manent magnet being polarised radiaily t "oughout its G-shaped length to present mags. ic oles of like polarity to the opnosite magnetic notes of the constant unidirectional held of said instrument, the flux strength oi said 3=shaped magnet being graduated along its iii-shaped iengtn and said C-shaped magnet being rotatable with respect to the constant unidirectional field producing means with the coil member oi the instrument whereby said -shaned magnet develops rotary torque with respect to such imidirectional field producing means within the measurement range of operation of said instrument.

9. In aneiectricai measuring instrument having a permanent magnet rotary bar armature member establishing the axis of rotation of the instrument, a pointer moved by said armature, a stationary scale cooperating with said pointer, and a stationary coil with which said armature cooperates ior electrical measurement purposes when the coil is energized and an auxiliary torque pull-off magnet for moving the pointer to an ofl-scale position when the coil is not energized,

terial coaxial and surrounding the axis of rotation of the instrument outside of its permanent magnet armature and within the influence of said armature, said C-shaped member bein permanently magnetized in a radial direction throughout its C-shaped length so as to present a pole of one polarity to the poles or opposite magnetic polarity of the armature throughout the range of deflection of the instrument, said c-shaped magnet producing permanent magnet flux strength which is a maximum at the center yoke portion thereof and which becomes less toward its open ends, and the center or said C- shaped magnet being positioned so as to rotate the armature to an ofl-scale pointer position when said stationary coil is not energized.

' v RICHARD G. JEWEL-L. 

